I'm having a very confusing issue.

I have a 1996 Ski Nautique with the Throttle Body PCM Chevy 5.7/350

I was out on the water late last year and was returning to the boat launch when I heard a "pop" at the rear of the engine and had complete electrical power loss.

Got the boat home and didn't start to mess with it until a couple of weeks ago.

Due to several other things going on I replaced the following parts.

Battery (Battery tender said it was bad)

50amp push breaker at the rear of the engine

Starter relay

Had the starter rebuilt.

The problem I am having now is when I try to turn the key over for ignition, I immediately lose power to the dash and the back of the engine has a little "click". I checked the push breaker for continuity and to see if it was blown and it was not. Power returns between 5-20 minutes later but when I try to turn the key over, the same thing happens. 

I'm confused as to why I would intermittently lose power for a period of time and then for it to come back on later just to repeat the issue.

My next thought is to replace the ignition switch.

If anyone has a wiring diagram for this boat that would be awesome, But I can't seem to find one.

Does anyone have any suggestions? 

Thanks!

If you click on the link below and go to page MT17 you'll have a PCM wiring diagram for the engine, not including the injection side of things. Not the best, but better than nothing

It's from the CCF reference section